A profile (e.g., extruded profile) formed of aluminum or an alloy thereof (hereinafter referred to as “aluminum alloy”) and having an irregular cross-sectional shape has been used in a wide variety of fields (e.g., building materials, vehicular parts, and daily commodities).
A profile formed of an aluminum alloy or the like is normally anodized in order to improve surface properties such as corrosion resistance and hardness.
However, since it may be unnecessary to form an anodic oxide coating over the entire surface of the profile, a method that forms an anodic oxide coating on part of the surface of the profile has been proposed.
For example, the Applicant of the present application proposed a method that quickly forms an anodic oxide coating on an aluminum alloy extruded profile having an irregular cross-sectional shape only within a specific range in the longitudinal direction (see JP-A-2005-68458).
On the other hand, the present invention was conceived to form an anodic oxide coating on part of the outer surface of a profile in a cross direction.
JP-A-5-25693 and JP-A-11-117092 and the like disclose a method that forms an anodic oxide coating only on the inner side of a hollow aluminum product. However, an apparatus and the like that partially anodize the outer surface of a profile having an irregular cross-sectional shape have not been proposed.